FIGS. 5(a)-5(d) are cross-sectional views showing a prior art production method of a Schottky barrier diode. In FIG. 5(a) reference numeral 1 designates a semiconductor substrate. An insulating film 2 is produced on the semiconductor substrate 1. A metal film 3 is provided on the semiconductor substrate 1 to produce one electrode of the Schottky barrier diode. Reference numeral 7 designates an aperture of the insulating film 2. The other electrode of the Schottky barrier diode is not shown here.
The production method of the Schottky diode is described with reference to FIGS. 5(a) to 5(d).
As shown in FIG. 5(a), a semiconductor substrate 1 is prepared. As this semiconductor substrate 1, for example silicon monocrystal is used.
Next, as shown in FIG. 5(b), an insulating film 2 is produced on the semiconductor substrate 1 by such as thermal oxidation or chemical vapor deposition. As this insulating film 2 silicon dioxide (SiO.sub.2) is used.
Next, as shown in FIG. 5(c), an aperture 7 is produced on the insulating film 2 at a portion on the semiconductor substrate 1 corresponding a portion where a Schottky barrier diode is to be produced. The production of this aperture can be easily performed by, for example when the insulating film is silicon dioxide film, producing a pattern of photoresist film on the silicon dioxide film by photolithography and etching the silicon dioxide film with a hydrofluoric acid solution using this photoresist film as a mask. By removing the photoresist film with sulfuric acid or an oxygen plasma after the etching, an aperture 7 is produced at the silicon dioxide film 2.
Then, as shown in FIG. 5(d), a metal thin film 3 is produced on the semiconductor substrate 1 in the aperture of the insulating film 2 and a Schottky barrier diode is thus produced. As a production method of this metal thin film 3, an electron beam deposition or sputtering is employed.
When platinum silicide is used for the metal film 3 and silicon is used for the semiconductor substrate 1, when annealing is performed after the platinum film is produced on the entire surface, the platinum in contact with silicon is silicided to produce platinum silicide, and when it is immersed in aqua regia after the annealing, platinum which is not silicided on the insulating film 2 is dissolved by the aqua regia and a metal side electrode of Schottky junction is selectively produced only at the aperture where the silicon substrate is exposed.
Because the Schottky diode is an element having a junction between the surface of a semiconductor substrate and a metal film in contact therewith, it is strongly influenced by the state of surface of the semiconductor and the crystallinity of semiconductor substrate in the vicinity of the surface. Accordingly, processes producing low contaimination and damage are required to be used for producing the insulating film 2 on the semiconductor substrate 1, for producing an aperture on the insulating film 2, and for producing metal electrode 3 of the Schottky diode.
Wet etching methods which have been utilized conventionally are those for removing material by using chemicals utilizing a chemical reaction at the liquid phase-solid phase interface. Those methods etch selectively between materials, have good processing ability, and do not damage the substrate. However, when this method is employed for producing a pattern, so-called transverse etching in which the etching advances with the solution circulating below the etching mask is likely to arise. Particularly when a photoresist which is inferior in adhesiveness to respective kinds of films constituting a semiconductor device is used, such transverse etching cannot be avoided.
When a Schottky barrier diode of FIG. 5(d) is integrated in integrated circuit, the film thickness of the insulating film 2 has to be approximately 1 micron in thickness in order to reduce the parasitic capacitance. When an aperture is to be produced on such a thick insulating film by utilizing a wet etching, etching in the transverse direction is large and a fine pattern is not obtained.
In recent fabrication process of semiconductor devices dry etching is used especially for monocrystalline silicon, polycrystalline silicon, silicon dioxide films, and aluminum films. Of dry etching processes, those utilizing reactive ion etching are advancingly developed.
These methods permit etching close to the dimension of a mask pattern because an etching reaction arises with reactive ions being accelerated in a direction perpendicular to the substrate surface and the etching amount in the transverse direction is small, so that a wide range of application is possible including to photoresist which has less adhesiveness to respective kinds of films constituting the semiconductor device, and to miniaturization of a pattern. As a result of that, it is possible to use a positive type photoresist and an apparatus of the step and repeat type can be used as an exposure apparatus in the photolithography, thereby enhancing the mask alignment precision where different kinds of films in the semiconductor device are successively processed using photoresist as mask material.
However, in RIE, etching is performed by reactive ions colliding with the film to be etched and damage accompanying the collision of ions and contaminations due to attachment of ions which do not participate in etching occurs.
Schottky barrier diodes are quite weak to the contamination of surfaces and defects in the vicinity of surface because they use a junction at an interface between the surface of semiconductor and the metal in contact therewith. Particularly in a device using a thin film of platinum silicide about 50 angstroms thick as in an infrared detecting element using a Schottky barrier diode of platinum silicide and silicon, the interface between the silicide and silicon is likely to be influenced by the silicon surface and it may become impossible to detect the infrared due to damage in silicon substrate. Thus, in the prior art device it was impossible to employ RIE for aperturing the insulating film 2 which is produced on the substrate 1.
Further, methods utilizing the above-described wet etching method and RIE in which a hole is dug through the insulating film 2 and thereafter an aperture is provided by wet etching is thought of. However, the etching speed by RIE easily varies dependent on the process conditions such as pressure and is difficult to control. Therefore, it is likely to cause variations in the depth of the apertures 7a to 7d of the insulating film 2 which is produced by RIE as shown in FIG. 6 caused by non-uniformity of etching speed in wafer surface over the entirety of the etched material, non-uniformity of the film thickness, variations in the film thickness of the etched material whereby the wet etching after the RIE cannot be performed uniformly.
As discussed above, in the prior art production process of a semiconductor device, there is a problem in that when a wet etching is used to produce an aperture in an insulating film on a substrate, a fine pattern is not obtained because of etching in the transverse direction and there is also a problem in that the RIE is inappropriate for production of a Schottky barrier diode because it damages the surface of substrate at the interface of Schottky junction and deteriorates the element characteristics. Further, in a method using RIE and wet etching for the production of an aperture of an insulating film, the etching by RIE cannot be performed uniformly in wafer, and the wet etching process thereafter cannot be performed with high controllability.